1. Technical Field
This invention generally relates to screen printing apparatus, commonly known as silk screening apparatus, and more particularly, this invention relates to an adjustable and retensionable screen frame for industrial use.
2. Background Art
One of the more common and most versatile of the printing processes is that of screen printing, or more commonly known as silk screen printing. Screen printing can be used to print on paper products, wood, plastics, textiles, etc. One of the most versatile industrial uses of screen printing is the printing of designs on textiles used in clothing, home decorating and the like. Because of the extreme versatility associated with the screen printing process, screen printing is the method of choice for a wide variety of mediums. Also, the screen printing process is well suited for printing designs on textile articles after they have been assembled, e.g., shirts, uniforms, hats and the like. This is the primary concern of the instant invention.
When printing detailed designs and/or multi-colored designs on a textile product, it is imperative that the printing screen be held extremely taut to insure accurate registration of the fine detail and/or various colors. The prior art solutions to this problem can be classified into three general categories. The first prior art solution, which is only a partial solution, has the screen material, typically nylon or polyester, glued under tension to a wooden perimeter frame. It is fairly common to have the screen pre-tensioned under the specific factory requirements during the gluing process. Unfortunately, screens tend to relax over time and consequently less workable tension is left in the fabric. Sometimes this occurs even before the screen is used on the production line.
A second prior art solution involves an adjustable tension frame which uses tension rollers along the frame sides to tension the screen material. This frame is commonly known as the Newman Roller Frame available from Stretch Devices, Inc. of Philadelphia, Pa. While these devices work well, they are extremely expensive.
A third prior art solution represents a compromise between the first two and consists of a floating bar type frame. Floating bars are suspended around the inner perimeter of the frame by traveler screws and wing nuts. Once the screen material has been attached to the floating bars, the wing nuts are tightened drawing the floating bars closer to the frame away from the center of the screen material, thus tightening the screen. Unfortunately, the floating bars occupy a significant amount of space within the interior of the frame and therefore limit the design space area. Additionally, the double frame configuration is quite heavy. In order to print a larger design, the printer must use the next available larger frame size and consequently an excessive amount of screen material, which is quite expensive.
An additional problem with tensioning the polyester screen material, is that as it is tensioned both laterally and longitudinally, extremely high tension stresses are developed in the corner pocket areas. As a result, the screen often tears and is rendered useless.
What is needed is an adjustable tension screen printing frame which is inexpensive to construct and which does not require an excessive amount of screen material to implement a particular design and which can be retensioned after use to maintain original factory tension specifications. It is therefore an object of the instant invention to provide an adjustable tension screen printing frame which is of a simple and inexpensive construction and which optimizes the amount of available screen area to accommodate large designs. It is an additional object of the instant invention to eliminate tearing of a retensionable polyester screen by reducing the stress in the pocket areas.